This invention relates to an improvement of a damper device for gradually closing a door, which is formed integrally with hinge pieces.
The following device for gradually closing a door is known in the art:
The device is provided with the upper and lower cylinders whose adjacent opening ends are rotatable in close contact with each other and which are formed integrally with hinge pieces fixedly secured to the door, respectively, a piston operation member closely fitted into the upper cylinder in such a manner that it is rotatable with respect to the upper cylinder, and a piston member the rotation around its axis and the vertical movement of which are guided by a guide member provided in the cylinder as the piston operation member is rotated. The guide member is provided with a multi-thread section. The piston member is provided with a multi-thread section corresponding to the multi-thread section of the guide member. In the lower cylinder are provided a plurality of chambers which are divided into the upper and lower chambers by the piston operation member. The chambers are filled with viscous fluid such as oil. A through-hole is formed in the axial portion of the piston member so as to communicate with the chambers, and in addition another through-hole provided with a check valve is formed to communicate with the chamber. The rotation and vertical movement of the piston member is controlled by the two through-holes and a rod extended from the piston operation member, which passes through the two through-holes.
In the conventional damper device thus constructed, if in order to vertically move the piston member by the piston operation member which is rotated in association with the swing of the door, the stroke of vertical movement of the piston member is increased with respect to the swinging angle of the door, that is, the rotation angle of the piston operation member, the damping force will be increased. However, in this case, it is necessary to modify the thread section of the guide member in which the piston member is screwed, into a multi-thread structure.
However, the process of forming the thread section on the outer wall of the guide member as a multi-thread section is rather troublesome or difficult. In addition, since viscous fluid such as oil is contained in the guide member, it is necessary that the guide member provided with the multi-thread section is retained at the top, and accordingly it is necessary to weld a separate piece thereto. Thus, the conventional damper device is disadvantageous in that the manufacture there-of is rather difficult, and the manufacturing cost is relatively high, that is, the damper device is not economical in the point of view of manufacture.